Reference is made to U.S. Pat. No. 4,828,335, assigned to the assignee of the present invention, illustrating a hydraulic control module for a vehicular antilock braking system, the subject matter of which is incorporated herein by reference. The module includes a number of solenoid-actuated hydraulic control valves generally serving the purpose either of isolating the flow of pressurized hydraulic fluid from the master cylinder to the brake cylinder or of dumping hydraulic fluid from the brake cylinder to an accumulator, which automatically supplies brake fluid at a pressure sufficient to reapply the brake at that particular cylinder to thereby assist in maintaining a controlled braking of the vehicle.
Each of these valves, namely the isolation valve and the dump valve, include an annular lip seal fitted within a valve cartridge and sealing it relative to a bore of a housing within which the valve cartridge is located, doing so in a manner that prescribes a fluid flow path through and around the valve to and from other hydraulic lines within the housing. Looking to the isolation valve, for example, the lip seal is located on the valve cartridge within the housing bore intermediate the valve inlet from the brake pedal and the valve outlet leading ultimately to a brake cylinder at the vehicle wheel.
The lip seal must function as (i) a check valve to preclude fluid flow between the valve and the housing bore from the inlet of the valve to the outlet of the valve, and (ii) as a flow valve or pressure relief valve for permitting flow of brake fluid from the brake cylinder and accumulator during brake release so that the normally open isolation valve is permitted to open in its conventional manner rather than be forced closed by the unrelieved pressure of the brake fluid from the brake cylinder.
Conventionally, for the purpose of providing a flow valve, as shown in U.S. Pat. No. 4,828,335, the outer extremities of the seal are provided with numerous axially extending and angularly equidistantly spaced ribs, with the passage between each pair of adjacent ribs defining a flow path for brake fluid to flow past the seal lip from the master cylinder side during brake release.
However, during conditions of extreme pedal pressure being applied to the brakes, this increased fluid pressure within the annular groove retaining the lip seal may force the lip seal to the low pressure side of the annular groove and place it under significant compression.
This can result in the valves experiencing a lock-up condition wherein the annular lip symmetrically deforms and is held fast to the valve bore with no space into which it can escape to allow fluid flow through the bore and resultant pressure release across the valve outlet to allow the isolation valve to open.
As a related matter, there has been great interest in downsizing the hydraulic control module, primarily for saving space and weight. If the radial cross-sectional area of the lip seal can be decreased, for example, if the inside diameter of the seal can be maintained while decreasing the outside diameter of the seal to accommodate a valve cartridge of given diameter within a smaller diameter bore, then the opportunity presents itself for downsizing an entire hydraulic control module.